In the prior art, a chain drive system for driving auxiliary machinery used to transmit rotation of a crankshaft of an engine to a cam shaft or the like has a construction such as shown in FIGS. 3 to 6.
The system shown in FIG. 3 has the simplest structure where a chain 23 is stretched between one driving sprocket 21 and one driven sprocket 22. When the driving sprocket 21 is driven for rotation, a slack run 23A of the chain 23 slackens slightly and a tension run 23B is pulled linearly due to rotational resistance of the driven sprocket 22 and the power transmission is performed.
The system shown in FIG. 4 has a chain 33 stretched between one driving sprocket 31 and two driven sprockets 32A, 32B creating one slack run 33A and two tension runs 33B, 33C of the chain 33. All of the runs respectively engage fixed guides 34A, 34B, 34C having shoe surfaces slightly bowed in convex circular arc shape and slidably contacting slidable the chain 33. Swinging of the chain 33 during running is prevented by the fixed guides.
The system shown in FIG. 5 uses one driving sprocket 41 and one driven sprocket 42 in similar manner to that in FIG. 3, but a tensioner 44 is arranged on the slack run 43A of the chain 43, while the tension run 43B is guided by a linear fixed guide 45. In the tensioner 44, a tensioner lever 44B pivotally supported by a fixed support shaft 44A has a shoe surface pushing against an outside surface of the slack run 43A of the chain 43 by biasing force of a torsional coil spring 44C, thereby providing tension to the chain 43.
Further the system shown in FIG. 6 has a chain 53 stretched between one driving sprocket 51 and two driven sprockets 52A, 52B in a manner similar to that in FIG. 4, and a shoe 54A of a tensioner 54 is pushed against a slack run 53A and slackening of the chain 53 is prevented. Also two tension runs 53A, 53C of the chain 53 are guided respectively by two fixed guides 55A, 55B having shoe surfaces slightly bowed in convex circular arc shape.
When the chain drive system for driving auxiliary machinery in the prior art as shown in FIGS. 3 to 6 is used in an engine with rotation variation being large, for example, a Diesel engine, since the rotation variation is large in a driving sprocket provided at a crankshaft, there is a problem that impact force caused by the rotation variation acts on the chain and excessive tension is applied in pulses to the chain at tension run which is guided by fixed guides.